Oxide proton conductors are of great interest for their application in solid oxide fuel cells. Yttrium-doped barium zirconate (BZY) has high grain (bulk) proton conductivity at intermediate temperatures (e.g., 400-600° C.), and it has good chemical stability toward moisture and carbon dioxide. However, it is difficult to sinter BZY to high densities, and it has high grain boundary resistivity. BZY requires very high sintering temperature (≧1600° C.) to obtain high density (i.e., a low-porosity or nonporous film). The use of high sintering temperatures can increase density and enhance grain growth, which reduces the number of grain boundaries and increases the grain boundary conductivity, thereby increasing the total conductivity of BZY. High sintering temperatures, however, can promote deleterious chemical reactions between BZY and its electrodes. It can also accelerate the evaporation of barium oxide, which degrades the electrolyte's conductivity.
Yttrium-doped barium cerate (BCY) has the highest total conductivity among the reported perovskite oxides and has good sinterability (i.e., it can be sintered at relatively low temperatures≦1400° C.). In spite of its favorable transport properties, BCY has poor chemical stability toward CO2 and water, which are present in fuel cell anode gas. There is an ongoing need for proton-conducting ceramic electrolytes and anodes for fuel cell applications, which have favorable transport and chemical stability properties. The solid electrolytes and electrodes described herein address this need.